NLO tools and the background to H→WW

A theory input is needed for the estimation of the largest background for the H→WW search at the LHC. This is the shape of the mℓℓ spectrum from continuum WW production. We find this to depend on how NLO matrix elements are merged with parton showers, and we compare the results from a number of different implementations. The results suggest that both the size of the background estimate and its uncertainty may have been underestimated. This conclusion is reinforced by a Note added, which comments on the LHC results released on November 14, 2012.